1. Field of the Invention
The present invention relates, generally, to a piston and connecting rod assembly for an internal combustion engine, and, more specifically, to such an assembly including a bushingless small-end connecting rod having a phosphatized coating for use with a profiled piston pin to improve wear of the piston/connecting rod pivot point and reduce deformation of the pin bore.
2. Description of the Related Art
Internal combustion engines known in the related art may generally include, among other basic components, an engine block having one or more cylinders, cylinder heads associated with the engine block and pistons supported for reciprocal movement in each cylinder. The piston generally includes a body having a crown and a skirt that depends from the crown to define the bottom half of the body of the piston. A pin bore is formed in the skirt. The pin bore corresponds to a similar bore at one end of the connecting rod. A pin is placed through the corresponding bores to attach the piston to the connecting rod. The end of a connecting rod having the piston pin bore is commonly referred to as the “pin end” or “small end.” The other end of a connecting rod is fastened to the crankshaft at a particular location. This end of the connecting rod is commonly referred to as the “crank end” or “large end.”
Generally, fuel is combusted within the cylinders to reciprocate the pistons. The piston drives the connecting rod, which drives the crankshaft, causing it to rotate within the engine block. Specifically, the combustion pressure within the cylinder drives the piston downward in a substantially linear motion. Focusing on the movement between the piston and the connecting rod, the term “top dead center” refers to the location of the piston at its uppermost point of reciprocal travel relative to the cylinder and is a point at which the piston is at a dead stop or zero velocity. Correspondingly, the term “bottom dead center” refers to the location of the piston at its lowermost point of reciprocal travel relative to the cylinder and is also a point at which the piston is at a dead stop or zero velocity. During movement of a piston from top dead center to bottom dead center on the powerstroke, the angle of the connecting rod produces a force component on the side of the piston commonly referred to as, “major thrust side.” On the other hand, during return movement of a piston from bottom dead center to top dead center produces a force component on the side of the piston commonly referred to as, “minor thrust side.” As fuel is combusted within a cylinder, the piston's reciprocal powerstroke and return movements drive the small end of the connecting rods in a substantially linear but slightly rotational motion. On the other hand, the large end of the connecting rod is attached to the crankshaft, which drives the large end of the connecting rod in a substantially rotational motion.
The combined linear and rotational movement of the connecting rod imposes a high level of stress on both the large end and small end pivot points. As between the two pivot points, the small end pivot point receives the greatest amount of stress, since it is adapted to facilitate angular movement of the connecting rod relative to the piston pin and piston skirt during the cycle from top dead center to bottom dead center and back. The combination of high loads, temperature, gas pressure and inertial forces localized at this pivot point requires that the small end of the connecting rod retain heightened properties relating to strength, wear, thermal stress and lubrication.
Stress imposed upon this pivot point may deform the piston pin, piston pin bore, and small end of the connecting rod. As a result of this deformation, the pivot point between the pin bore and connecting rod small end begins to scuff and wear. Scuffing in this area may lead to destruction of the pivot point and engine failure.
To counter the high loads imposed upon this pivot point, and to reduce friction and facilitate smooth angular movement, bronze bushings are typically employed between the bore of the small end of the connecting rod and the piston pin. The bushings reduce friction and facilitate smooth angular movement at this pivot point, thereby reducing deformation. However, bushings add weight to this pivot point and also require additional steps in manufacturing and assembly, both of which are generally undesirable.
Attempts have been made in the art to eliminate the bronze bushing from the assembly. For example, U.S. Pat. No. 5,158,695 issued to Yashchenko et al. on 27 Oct. 1992, discloses a material composed of copper, zinc, tin and diamond powder that is used in place of the conventional bronze bushings. However, the material disclosed in the '695 patent is applied to the piston pin and piston skirt but not to the connecting rod. Furthermore, in cases where bushings are not used, they are generally limited to either a diesel engine or for use with a non-profiled piston pin.
Accordingly, while the piston and connecting rod assemblies of the type known in the related art have generally worked for their intended purposes, they suffer from disadvantages relating to facilitating smooth angular movement at the pivot point while reducing weight in an internal combustion engine. As a result, there is an ongoing need in the art to improve the interface between the piston pin and the small end of the connecting rod, in general. Specifically, there is an ongoing need to reduce weight and streamline manufacturing process steps while retaining strength and acceptable product life of piston/connecting rod assemblies. Thus, there continues to be a need in the art for an improved piston pin and connecting rod assembly that is both lighter and stronger than previous generations of this assembly that still maintains good friction and wear properties.